Predictors of coronary bypass grafting in a population of middle-aged men.

BACKGROUND: Coronary bypass grafting is a procedure which is usually undertaken because of extensive coronary heart disease, whereas acute myocardial infarction may occur with patients with moderate or even minimal disease. Having undergone coronary bypass grafting may thus serve as a marker for extensive coronary atherosclerosis. The aim of this study was to assess risk factors for future coronary bypass grafting as a first coronary event, and to compare them with risk factors for a first acute myocardial infarction. DESIGN: This was a prospective cohort study. METHOD: In the Multifactor Primary Prevention Study, 7388 men aged 47-55 years and free of previous acute myocardial infarction or stroke were investigated between 1970 and 1973. During 28 years of follow-up 1664 men (22%) had an acute myocardial infarction or died from coronary disease. One hundred and forty six men (2%) underwent coronary bypass grafting with no prior acute infarction. RESULTS: Serum cholesterol was a stronger predictor of coronary bypass grafting than of acute myocardial infarction. Compared to men with serum cholesterol of 5.0 or lower, men with serum cholesterol 5.1-6.4, 6.5-7.4 and over 7.4 mmol/l had age-adjusted hazard ratios for acute myocardial infarction of 1.22 (1.00-1.49), 1.66 (1.35-2.03) and 2.04 (1.65-2.51). Corresponding hazard ratios for coronary bypass grafting were 1.57 (0.66-3.70), 3.44 (1.47-8.03) and 5.21 (2.20-12.31) (95% confidence interval). In contrast, smoking was a weaker risk factor for coronary bypass grafting than for acute myocardial infarction with no discernible increase in risk except in very heavy smokers (25 g/day or more; n=193); hazard ratio 2.19 (1.02-4.66). Elevated blood pressure predicted coronary bypass grafting and acute myocardial infarction equally well. In multivariate analysis an increase in serum cholesterol of 1 mmol/l was associated with an odds ratio of 1.56 (1.38-1.76) for coronary bypass grafting but only 1.30 (1.24-1.36) for AMI (P for difference in odds ratio 0.004). CONCLUSION: Elevated serum cholesterol is a stronger predictor for future coronary bypass grafting than for acute myocardial infarction. Moderate smoking was not associated with coronary bypass grafting. Different manifestations of coronary disease have different risk factor patterns, suggesting that secular changes in risk factor pattern could potentially influence the clinical expression of the disease.